Use an electric mixer to cream together Finlandia butter with granulated sugar and sea salt, about 2 minutes. Add the egg yolks and vanilla and beat on medium speed until light and fluffy, about 2 minutes more.
In a separate bowl, sift together the flour and baking powder, then add to the butter and mix until just incorporated. Don’t over-mix or it will make the cookies tough. Wrap the dough in plastic and refrigerate for at least one hour or overnight.
Preheat the oven to 350 degrees. Cut the dough in half, then place one half in between two pieces of parchment paper and roll out to be between 1/4 and 1/8th inch thick. Use a round cookie cutter to cut out circles, then transfer them to a parchment lined baking sheet about 1 inch apart. This is easiest to do when the dough is chilled, so place it in the refrigerator or freez-er between steps as needed. Re-roll the scraps and cut out more circles until you’ve used up all the dough.
Brush the cookies lightly with the beaten egg, then sprinkle with raw sugar. Bake for 12-15 minutes or until golden brown, rotating the pan half way through if not browning evenly.
Allow cookies to cool for one minute on the baking sheet, then transfer to a rack to cool com-pletely. Serve immediately or store in an airtight container at room temperature for up to 10 days.
Makes about 30 cookies.